arm: stm32mp: add support of STM32MP13x

Introduce the code in mach-stm32mp and the configuration file
stm32mp13_defconfig for the new STM32MP family.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/board/st/stm32mp1/Kconfig b/board/st/stm32mp1/Kconfig
index 89e97ae..6ab8f80 100644
--- a/board/st/stm32mp1/Kconfig
+++ b/board/st/stm32mp1/Kconfig
@@ -11,3 +11,18 @@
 
 source "board/st/common/Kconfig"
 endif
+
+if TARGET_ST_STM32MP13x
+
+config SYS_BOARD
+	default "stm32mp1"
+
+config SYS_VENDOR
+	default "st"
+
+config SYS_CONFIG_NAME
+	default "stm32mp13_st_common"
+
+source "board/st/common/Kconfig"
+
+endif